In a mobile communication system, a radio communication environment of a radio base station is changed due to construction of a building near the base station, change of an installation state of a neighboring base station of the base station or the like. For this reason, operators have conventionally performed drive tests in which reception states of signals from the base station (hereinafter, referred to as “radio states”) are measured to collect the measurement data by using a measurement vehicle with measurement equipment mounted thereon.
Such measurement and collection can contribute to optimization of coverage of the base station, for example, but have problems of requiring many man-hours and high cost. Hence, the 3GPP (3rd Generation partnership project) which is a standardization project for mobile communication systems has been developing specifications of MDT (Minimization of Drive Tests) for automatically performing the measurement and the collection by using user terminals carried by users (see Non-patent document 1).
One of MDT methods is logged-type MDT (hereinafter, appropriately referred to as “Logged MDT”). According to the current specifications for Logged MDT, the user terminal in an idle state measures a radio state according to measurement configuration information set by a network, logs a measurement result together with location information and time information as measurement data, and reports the logged measurement data to the network later.
In addition, another MDT method is immediate-report-type MDT (referred to as “Immediate MDT”). According to the current specifications for Immediate MDT, the user terminal in a connected state measures a radio state according to measurement configuration information set by a network, sends the network a report as measurement data including a measurement result and location information.
As described above, according to the current MDT specifications, the user terminal performs measurement of the radio state, that is, measurement on a lower layer (a physical layer). The network collects the measurement data acquired by such measurement, and thereby identifies a dead zone (a coverage hole) thus to achieve coverage optimization such as solving a problem of the coverage hole.